Question

Is this bit of code safe?

int main() {

    struct {
        int foo;
        int bar;
        std::list<...>::iterator it;
    } foobar;

    memset(&foobar, 0, sizeof(foobar));

    foobar.it = ...;
}

I’m thinking it’s safe because std::iterator doesn’t seem to override operator=. Is this a valid reasoning?

Answer 1

No. Assignment operator generally assumes that its left-hand side (recipient) operand has a valid state before assignment.

Meanwhile, you are steamrolling these zeros over possibly non-trivially constructed object of std::list<...>::iterator type. This can only work what you have intimate knowledge about the exact properties of std::list<...>::iterator and you know that filling it with zeros produces a valid object.